I have seen z80, z80a, and z80b processors, and I'm curious about what the differences are between the different versions of the processor? Is each newer version faster than the earlier model, like a 486-33/66/100 or are the differences more along the lines of additional commands (or something like that?) Or a combination of both? Also, can I use a Z80a or Z80b in place of the original Z80 if I want to replace a bad CPU? Thanks. E.